Expand the devtools/common readme.
Fixes domokit/devtools#1.
R=tonyg@chromium.org
Review URL: https://codereview.chromium.org/1158323008
Cr-Mirrored-From: https://github.com/domokit/mojo
Cr-Mirrored-Commit: eaf6dddef106a7f46abf3b78db9362206e684e89
diff --git a/README.md b/README.md
index 07d6db8..2e06256 100644
--- a/README.md
+++ b/README.md
@@ -2,8 +2,39 @@
Unopinionated tools for **running**, **debugging** and **testing** Mojo apps.
+The repo consists of:
+
+ - **devtoolslib** - Python module containing the core scripting functionality
+ for running Mojo apps: shell abstraction with implementations for Android and
+ Linux and support for apptest frameworks
+ - executable scripts - example embedders of devtoolslib and other utils
+
+## Embedding devtoolslib
+
+As devtools carry no assumptions about build system or file layout being used,
+the primary way of using devtools now is to embed the functionality provided by
+**devtoolslib** in a thin wrapper script. For examples, one can refer to mojo's
+[shell
+runner](https://github.com/domokit/mojo/blob/master/mojo/tools/mojo_shell.py)
+and [apptest
+runner](https://github.com/domokit/mojo/blob/master/mojo/tools/apptest_runner.py).
+
+## Executable scripts
+
+The set of executable scripts is WIP. We currently offer:
+
+ - **debugger** - allowing to send commands to the mojo:debugger app running in
+ the shell, allowing e.g. to interactively start and stop tracing
+
## Install
```
git clone https://github.com/domokit/devtools.git
```
+
+## File location
+
+The library is canonically developed [in the mojo
+repository](https://github.com/domokit/mojo/tree/master/mojo/devtools/common),
+https://github.com/domokit/devtools is a mirror allowing to consume it
+separately.
